Exemplary embodiments of the present invention relate to a sub master cylinder and a brake apparatus having the same, and more particularly, to a sub master cylinder which can reduce a pressure acting area in a master cylinder to decrease a driver's pedal actuation force while providing a braking force equal to or increased in comparison with the conventional art, and a brake apparatus having the same.
In general, a brake apparatus of a vehicle indicates a device for decelerating the speed of or stopping a traveling vehicle.
The brake apparatus operates in such a way as to perform a braking function through converting the kinetic energy of a vehicle into thermal energy by using a frictional force generated by a driver's actuation force or by auxiliary power.
In a passenger car, a hydraulic type brake apparatus is generally adopted. In this type, the driver's pedal stepping force is converted, by way of a hydraulic pressure as an intermediate medium, into the braking force of wheels.
A background art related with the present invention is disclosed in Korean Unexamined Patent Publication No. 10-2010-0005919 (entitled “Master Cylinder”).
In a brake apparatus, a clamping force Fclamp can be calculated by the following equation.
      F    clamp    =            F      pedal        ×    Pedal    ⁢                  ⁢    Ratio    ×                  A        caliper                    A                  M          /                      cyl            .                              
In the conventional art, in order to decrease a driver's pedal actuation force Fpedal in the state in which the braking force of the brake apparatus is maintained, that is, the clamping force Fclamp is maintained, a Pedal Ratio has been increased or a caliper size Acaliper has been enlarged.
However, in the case where the Pedal Ratio is increased, the load applied to a pedal bracket increases and the pedal bracket is likely to be deformed by a moment. Also, in the case where the caliper size Acaliper is enlarged, the manufacturing cost is likely to be increased due to an increase in weight.
Therefore, it is required to solve these problems.